The objective of the study is to describe, by means of the electron microscope the exact morphological and histochemical alterations which occur in in utero nematode spermatozoa. To determine the significance and extent of these alterations in relationship to the time the spermatozoa have been present in the female uterus, the seminal vesicles of mature males as well as the uteri of females inseminated for known periods of time will be examined. This information will be used to determine if the in utero alterations of nematode spermatozoa are a necessary preliminary to fertilization and therefore comparable to the capacitation phenomenon reported in certain mammalian spermatozoa. With the understanding that past studies of nematodes have contributed significantly to our understanding of biological principles regarding fertilization and embryonic development, it is expected that the proposed investigation will be useful in formulating new concepts concerning the in utero gamete maturation and syngany which is of great interest to cell biologists at the present time. The proposed studies will be particularly useful both in determining how zygote formation is accomplished in species having acrosomeless spermatozoa and in formulating a broader concept of the capacitation phenomenon which is relatively unknown in invertebrate organisms.